Model Parents:

if you parent your items to the unbreakable predicates shown below. You can then use the comment commands to pull your custom models into game. Did I mention you will lose no default Minecraft items!

Unbreakable Predicates:

each predicate has a command comment. This can help you to pull the custom models you create.

You can leave the comments or remove them to make the .json file just a little bit smaller.

CUSTOM TEXTURES:

textures/item/nubx:

The nubx folder can also be renamed to custom or anything you like. I use nubx since its a short version of my name. This is a way for me to watermark the resource pack and model parents with my name. You may choose to just name this custom as there are other ways to watermark your creations.

I have placed the nubx folder into items but you can place this any where you like, so long as you have linked your custom_model.json to the location of your texture. You may even choose to make a few custom folders for your textures to organize them but this is not needed and in some cases can be more of a pain.